定语从句：
在句子中起定语作用的从句叫做定语从句.定语从句所修饰的词叫先行词,包括名词,代词和动名词.由哪种关系词引导出的定语从句由先行词决定.
在定语从句中where when 的用法：
(1)when 可以代替in/on which 引导时间定语从句.
例如 That was the year when he was born.
那是他出生的那一年.
Sunday is a day when people don't have to go to work.星期天是人们不用上班的一天.
（2）where可以代替in/on which 引导地点定语从句.
例如：Let's meet at the gate where you can see the panda.我们在能看到大熊猫的那个大门见面吧.
She is teaching at the university where her mother once studied.
她在她母亲曾经学习过的大学执教.
This is the birdge where you took photos.
这是你照相的那座桥.
（定语从句牵涉的句法太多了.这在高中只是提到皮毛,在大学一年级老师会详细讲到）